Failed to create Livy session for executing notebook.

Hi willmasse 

Thanks for using Microsoft Fabric Community.

Apologies for the issue that you are facing here.

The 401 Unauthorized Error is an HTTP status code error that represented the request sent by the client to the server that lacks valid authentication credentials.

Methods to rectify the error: The 401 Unauthorized error can be fixed by using any of the following ways: 

• Check The URL: Due to manual errors in typing the URL, the 401 unauthorized error may occur. Hence, checking the URL and rectifying the mistakes in it will fix the 401 error status.
• Flush the DNS: Errors in DNS also creates 401 error status sometimes. Therefore, clearing the DNS will also rectify this error. In Windows, the DNS can be flushed by typing ipconfig/flushdns in the command prompt and clicking on ENTER.
• Clear Browser Cookie: In some situations, the cookies may not work smoothly leading to improper server authentication. Thus, by clearing the cookies, the error can be rectified.
• Logging out and Logging in again: If you're authenticated via a session (like in a web app), it might have expired. Therefore, logging out and logging in again by providing the credentials may also rectify this error.

I hope this information helps. Please do let us know if you have any further questions.